SubDyn: add per-member discretization support to align meshes with HydroDyn - #3385
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Add optional per-member MDivSize parsing and resolve per-member MemberNDiv with global NDiv fallback. Refactor FEM discretization to use per-member divisions, cache MemberElemStart, and avoid max-width MemberNodes storage. Update output mapping and summary generation to reconstruct member node ordinals from connectivity and MemberElemStart. Register and document SD_2Beam_MixedDiscretization regression case and update r-test submodule pointer. Co-authored-by: GitHub Copilot <copilot@github.com>
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This PR is ready. Need to merge PR #3356 into
rc-5.0.1and mergerc-5.0.1intodevfirst.Feature or improvement description
This PR adds optional element-length-based discretization for beam member to SubDyn. In the SubDyn input file, the
MEMBERStable now accepts a new optional 8th column at the end calledMDivSize. It defines the maximum length in meters of the resulting equal-length elements after discretizing the member. Effectively, it behaves the same way asMDivSizein the HydroDyn input file.Each member can have a different
MDivSize. If omitted for a given member, that particular member will revert back toNDivelements as before. This allows for backward compatibility.MDivSizeis always ignored for non-beam members, including cables, rigid links, and spring elements, which are not subdivided.Internally, SubDyn initialization and output have been revised to support differing number of elements for each member. When requesting beam member nodal outputs (load and motion),
NodeCntmust be less than or equal toNDiv+1if default discretization based onNDivis used (MDivSizenot specified), or be less than or equal to the actual number of nodes belonging to that member after discretization based onMDivSize. Users can refer to the SubDyn summary file for the number of nodes belonging to each member.The primary purpose of this change is to simplify mesh alignment between SubDyn and HydroDyn for hydroelastic simulations. Aligned meshes between the two modules are recommended to ensure physical results. With this update, if a member has the same starting and ending joint coordinates and the same
MDivSizein the two module input files, the internal mesh nodes will also be aligned between the two modules. Additionally, if members have drastically different lengths in SubDyn, theMDivSizebased discretization is more appropriate compared to the uniform subdivision based onNDiv. The latter will either result in excessive discretization of short members or inadequate discretization of long members.Impacted areas of the software
SubDyn, docs, r-test
Generative AI usage
Co-authored-by: Microsoft Copilot copilot@microsoft.com
Test results, if applicable
No change to existing r-tests (all passed); added a new SubDyn module r-test called
SD_2Beam_MixedDiscretizationto demonstrate the new discretization capability for beams.